The primary aim of this proposed project is to determine how closely changes in the apparent location of sound in the median sagittal plane (MSP) corresponds to changes in the sound spectrum. This will entail several approaches: 1) The minimum frequency bandwidth required for maximal localization proficiency in the MSP will be ascertained. 2) Apparent location of sound at specific positions in the MSP will be simulated by modifying the sound spectrum of stimuli originating elsewhere in the MSP. 3) An acoustical manikin will be employed to simplify the measurements of SPL at the "ear drum" when sounds are positioned at different places in the MSP. 4) Patients with middle ear pathology and those fitted with artificial pinnae will be tested on their ability to locate sounds in the MSP. From these latter data, inferences will be drawn about the influence of the resonance properties of the external ear canal, and directional properties of the pinna on sound localization.